Metabolism

I think most people talk about metabolism as the rate their body burns calories at rest, which is determined by the amount of lean muscle mass you have and is therefore completely changeable...I'm pretty sure that the notion of a metabolism you are born with and leaves you just plain lucky or unlucky has been debunked though.

I can't send you links to prove it at the moment but I remember reading some scientific paper about a study that showed that the BMR of the participants in the trial of similar age, gender, weight and height was very similar. That is the BMR does not vary much if at all, opposite to popular beliefs. So the formulas for BMR you can find online are generally quite accurate. The variance comes mostly from otherwise burned calories, not metabolism.

A lot of the problem is that most of us has been spoon fed this metabolism stuff since we were little. I remember my mom telling people I had a slow metabolism when I was a chunky 11 year old. I always thought my metabolism was messed up for decades. It wasn't until I started MFP and started reading more about it that I realized that all the crap I've believed was wrong. All the stuff the media and diet "experts" said was wrong. My metabolism isn't slow or messed up. I was just lazy.

mdrichardsons wrote: »

Can you improve your metabolism or damage it? Make it so you can eat more calories and still maintain? Or is it only set by age?

Your base metabolic rate isn't the only thing that impacts how much you can eat and still maintain. Calorie burns from exercise and non-exercise activity are very easy to manipulate and are entirely within your control. I tend to believe that when you look at someone and think they have a "fast metabolism", you're almost certainly looking at someone with a normal metabolism and a high daily activity level.

FWIW, I personally tend to believe that the majority of people are within normal metabolic parameters, with the possible exception of people who have had drastic and fast weight loss or who are long-term yoyo dieters (if you lose fat+muscle, gain the fat back, and repeat over time, you eventually negatively impact your body composition).

http://www.precisionnutrition.com/metabolic-damage

Excerpts:


“Is my metabolism damaged?”
Can months or years of dieting do some kind of long-term harm to the way the human body processes food?
Not exactly.
But gaining and losing fat can change the way your brain regulates your body weight.

Losing weight won’t “damage” your metabolism.
But because of the adaptations your body undergoes in response to fat loss (to prevent that fat loss, in fact), ‘energy out’ for those who have lost significant weight will always be lower than for people who were always lean.
Rather:
Losing weight, and keeping it off, is accompanied by adaptive metabolic, neuroendocrine, autonomic, and other changes.
These changes mean that we expend less energy — around 5-10 percent less (or up to 15 percent less at extreme levels) than what would be predicted based on just weighing less.
Unfortunately, because of this adaptive response, someone who has dieted down will often require 5-15 percent fewer calories per day to maintain the weight and physical activity level than someone who has always been that weight.
(Or even less, potentially, because as we learned in the very beginning, the RMR of people of the exact same age/weight/etc. can still vary by up to another 15 percent.)
This means someone who was never overweight might need 2,500 calories to maintain their weight, while someone who had to diet down to that weight may need only 2,125-2,375 calories to hold steady.
We don’t know how long this lowered energy expenditure lasts. Studies have shown that it can hang around for up to 7 years after weight loss (or more, 7 years is as far as it’s been studied). This likely means it’s permanent, or at least persistent.
This is extra relevant for people who have repeatedly dieted, or for fitness competitors who may repeatedly fluctuate between being extremely lean and being overweight in the off-season.

All of this explains why some people can feel like they’ve “damaged” their metabolism through repeated dieting. (And why some experts suggest “metabolic damage” is a real thing.)
But nothing really has been “damaged”.
Instead, their bodies have just become predictably more sensitive to various hormones and neurotransmitters. Their metabolic rates are understandably lower than predicted by various laboratory equations.